1. Field of the Invention
The present disclosure relates to an internal combustion engine with variable valve opening characteristics.
2. Discussion of the Background
An increasing number of four cycle gasoline engines (hereinafter simply referred to as an engine) with various variable valve timing mechanisms have been proposed in order to achieve improvement in output and fuel consumption, and a reduction in the amount of toxic exhaust gas component. A variable valve timing mechanism which switches between a low-speed cam and a high-speed cam has been used to date, however, in recent years, a variable valve timing mechanism which achieves considerably improved transient characteristics, throttle-less operation, and the like by continuously and variably controlling a cam phase and a valve lift individually is becoming mainstream technology.
A Variable Timing Control Device (hereinafter referred to as a VTC) used for variable control of the cam phase includes a hydraulic actuator (hereinafter referred to as a VTC actuator) which is mounted near one end of a camshaft in a cylinder head, and a hydraulic pressure control valve which controls the oil pressure (engine oil pressure) supplied to the VTC actuator. A configuration is adopted in which the VTC actuator has a rotor with a plurality of vanes, and a housing which houses a rotor in a relatively rotatable manner, and the rotor and the housing are rotated relative to each other by supplying hydraulic fluid (engine oil) as needed to an advance angle chamber and a retard angle chamber which are formed in the housing. The rotor is fixed to the camshaft, while a cam sprocket is formed integrally with the housing (see Japanese Unexamined Patent Application Publication No. 2009-264133).
On the other hand, the present applicant has proposed an opening angle variable valve device which includes an intake camshaft in a double structure composed of a fixed outer camshaft, and a movable inner camshaft so as to allow an intake opening angle (a period between valve opening and valve closing) to be variably controlled by setting different phases of the outer camshaft and the inner camshaft using a phase change unit (a hydraulic actuator similar to the VTC actuator). In the device, a fixed intake cam formed in the outer camshaft, and a movable intake cam formed in the inner camshaft have the same cam profile, and when the phases of the outer camshaft and the inner camshaft are the same, the device operates similarly to a normal inlet cam, whereas when the phases of the outer camshaft and the inner camshaft are shifted with respect to each other (the inner camshaft is rotated relative to the outer camshaft), the high part of the fixed intake cam and the high part of the movable intake cam are arranged continuously in the circumferential direction, and thus the intake opening angle is increased (see Japanese Unexamined Patent Application Publication No. 2002-54410).